Avermectins are antiparasitic antibiotics produced by Streptomyces avermitilis. Four main ingredients (A1a, A2a, B1a and B2a) have been known, and among them, avermectin B1a is known to have potent activity (Japanese Patent Unexamined Publication (KOKAI) No. (Hei) 3-254678/1991).
Various derivatives have been synthesized so far to provide avermectin derivatives having higher activity. However, these derivatives fail to have fully satisfactory antiparasitic activity.